docs: def page_align_content_length(length):
      # type: (int) -> int
      """Compute page boundary alignment
      :param int length: content length
      :rtype: int
      :return: aligned byte boundary
      """
      mod = length % _PAGEBLOB_BOUNDARY
      if mod != 0:
          return length + (_PAGEBLOB_BOUNDARY - mod)
      return length